Download 12_Doppler (Mar 12)

Announcement
Test 2
is coming up on Mar 19.
Start preparing!
This test will cover the classes from Feb 27 - Mar 14.
50 points, scantron, 1 hr.
1
Lecture-Tutorial (LT):
Analyzing Spectra (pp. 69-72)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
•
•
•
one another.
Come to a consensus answer you both agree
on.
If you get stuck or are not sure of your answer,
ask another group.
If you get really stuck or don’t understand what
the LT is asking, ask for help.
2
AST 103
Doppler Shift
Prof. Ken Nagamine
UNLV
3
What can we learn by analyzing starlight?
• A star’s (or any other object’s) temperature
- peak wavelength of the spectral curve
• A star’s chemical composition
- dips in the spectral curve or the
lines in the absorption spectrum
• A star’s motion
4
The Doppler Effect
• Definition: “The change in wavelength due to
the relative motion between the source and
the observer along the line of sight.”
http://www.youtube.com/watch?v=Kg9F5pN5tlI
5
Astronomers use the Doppler Effect to learn
about the radial (along the line of sight) motions
of stars, and other astronomical objects.
6
Real Life Examples of Doppler Effect
•
•
•
•
Doppler Radar (for weather)
Airplane radar system
Submarine radar system
Radar gun, used by police officers
7
Doppler Effect
• When something that is giving off light moves
toward or away from you, the wavelength of the
emitted light is changed or shifted.
V=0
redshift
blueshift
8
The Doppler Effect
• Definition: “The change in wavelength of
radiation due to relative motion between the
source and the observer along the line of
sight.”
9
Doppler Effect
• “Along the line of sight” means the Doppler
Effect happens only if the object which is
emitting light is moving toward you or away
from you.
– An object moving “side to side” or
perpendicular, relative to your line of sight, will
not experience a Doppler Effect.
10
Application to Astronomy
The shift of spectral lines can tell the
motion of astronomical objects.
V=0
11
Doppler Shifts
• Redshift (to longer wavelengths): The source is
moving away from the observer
• Blueshift (to shorter wavelengths): The source is
moving toward the observer
Δλ = wavelength shift
λo = wavelength if source is not moving
v = velocity of source
c = speed of light
The amount of shift is proportional to the relative velocity.
12
What can we learn by analyzing starlight?
• A star’s temperature
- peak wavelength of the spectral curve
• A star’s chemical composition
- dips in the spectral curve or the
lines in the absorption spectrum
• A star’s motion
- Doppler shift
13
Lecture-Tutorial (LT):
Doppler Shift (pp. 73-77)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
•
•
•
one another.
Come to a consensus answer you both agree
on.
If you get stuck or are not sure of your answer,
ask another group.
If you get really stuck or don’t understand what
the LT is asking, ask one of us for help.
14
Quiz
The Doppler Effect causes light
from a source moving away to:
A)
B)
C)
D)
E)
be shifted to shorter wavelengths.
be shifted to longer wavelengths.
changes in velocity.
Both a and c above
Both b and c above
15
Quiz
You observe two spectra (shown below) that are redshifted
relative to that of a stationary source of light. Which of the
following statements best describes how the sources of light
that produced the two spectra were moving?
BLUE
RED
Spectrum A
Spectrum B
A)
B)
C)
D)
Source A is moving faster than source B.
Source B is moving faster than source A.
Both sources are moving with the same speed.
It is impossible to tell from looking at these spectra.
16
Quiz
A bright star is moving toward Earth. If
you were to look at the spectrum of this
star, what would it look like?
A)
B)
C)
D)
E)
an absorption spectrum that is redshifted relative to an unmoving star
an emission spectrum that is redshifted relative to an unmoving star
a continuous spectrum that is blueshifted relative to an unmoving star
an absorption spectrum that is blueshifted relative to an unmoving star
a continuous spectrum that is redshifted relative to an unmoving star
17